Nature 407, 582 - 583 (2000) © Macmillan Publishers Ltd.

Biomechanics: Asymmetric toes aid underwater swimming

L. CHRISTOFFER JOHANSSON AND ULLA M. LINDHE NORBERG

The unique morphology of the toes of the great crested grebe (Podiceps cristatus), which are asymmetrically lobed with a narrower skin flap on the lateral side of the toe, enables these birds to swim very efficiently. Here we study video recordings of a diving grebe and stroboscopic pictures of its moving feet and conclude that the bird uses a hydrodynamically lift-based foot (power) stroke to propel itself underwater, with the separated toes functioning as multiple slots to increase the lift-to-drag ratio. The asymmetric lobes are an adaptation for self-stabilization of the toes during the power stroke, and the toes themselves act as separate hydrofoils, each producing lift and each being twistable individually under hydrodynamic load.